Friday, August 19, 2016

The Case for Chilled Beams in Schools

We all know the importance of comfort in schools and
comfort’s relationship with student performance. While temperature gets the
lion’s share of attention, equally important are noise, humidity, and
ventilation. Efforts to update standards to address noise, humidity, and
ventilation have made it harder for traditional HVAC equipment to establish and
maintain comfortable learning environments in schools.

Enter chilled beams.

In a chilled-beam system, zone-based hydronic heating and/or
cooling devices complement the primary air ventilation system, enabling the
optimization of all heating, cooling, and ventilation functions. Chilled beams
are quiet, can reduce energy consumption and maintenance, and take up less
ceiling-cavity space while contributing to conditions that increase occupant
performance.

Noise

Think back to when you were a kid in math class. There
probably were a number of distractions: a class clown, paper airplanes, someone
passing notes.

One disruption that does not get the attention it deserves
is unnatural or excessive background noise, which studies have shown can significantly
hinder student performance. Conventional HVAC systems rarely meet prescribed
background-noise-level requirements. ANSI/ASA S12.60, Acoustical
Performance Criteria, Design Requirements, and Guidelines for Schools,
requires a maximum background-noise level of 35 dBA (about NC 27)—difficult, if
not near impossible, to attain with traditional classroom HVAC equipment.
Chilled beams do not rely on internal motors or blowers to recirculate and
recondition room air and, thus, can be utilized to maintain HVAC
background-noise levels in accordance with ANSI/ASA S12.60.

Humidity and Ventilation

HVAC systems that modulate supply airflow rate during
occupied operation often do not maintain outdoor airflow rate within the
requirements of ANSI/ASHRAE Standard 62.1-2013, Ventilation for
Acceptable Indoor Air Quality. Additionally, with all air systems, minimum
ventilation airflow rate establishes minimum supply airflow rate. During
off-peak operation, this airflow rate exceeds what is required for cooling,
necessitating the reheating of supply air before it enters a space.

Active chilled beams served by a dedicated outdoor-air
system (DOAS) utilize ducted variable-temperature outdoor air to induce room
air through an integral hydronic heat-transfer coil. Classroom cooling/heating
demand is met by modulation of the rate of water flow through the coil while
the rate of airflow remains constant. The coil’s effect on space conditioning
allows ducted-airflow temperature to be reset seasonally, resulting in
significant reheat energy savings.

Active beams can be located either within a ceiling grid or
floor-mounted adjacent to an outside wall. When active beams are floor-mounted,
ventilation air can be delivered to a classroom in a displacement-ventilation
manner. This method of delivery can reduce classroom carbon-dioxide levels and
the resultant risk of the spread of respiratory diseases by more than 50
percent.

Additional Benefits

Not only do chilled beams benefit students by being quieter
and more adept at adjusting to fluctuating humidity and heat conditions, they
benefit schools by reducing costs. While most conventional HVAC systems depend
on the delivery of large volumes of air to condition classrooms, chilled-beam
systems reduce ducted-air requirements by up to 60 percent by relying on their
integral heat-transfer coils to offset the majority of space sensible-cooling
and heating requirements. And because water is more efficient for space cooling
and heating than air, chilled beams use considerably less energy overall than
do other options.